Wastewater overflow consent

The Council is applying to Environment Canterbury for a new consent for wastewater overflows to waterways. This will allow the discharge of untreated wastewater to waterways during large storms, when the capacity of the wastewater network is exceeded.

The main purpose of a wastewater network is to protect public health, and to prevent people from coming into contact with raw wastewater. Constructed wastewater overflows to waterways act as safety valves on the wastewater network, so that when the network is overwhelmed in a large storm, wastewater does not overflow onto people’s properties or on the street.

Since 2010, Environment Canterbury (ECan) granted the Council consent for occasional overflows of wastewater to the environment during large storms. Due to earthquake damage and the likelihood there would be overflows more often than allowed, a non-enforcement agreement with ECan is in place. However, the Council needs to comply with its consent by September 2017, or apply for a new consent. The earthquake damage means that more stormwater and groundwater gets into the pipes than before. It seems unlikely that Council will be able to comply with its existing consent, so the process of applying for a new consent is underway.

The new consent will need to cover Christchurch (as at present) and Lyttelton and Akaroa harbours. Christchurch overflows are located on the Avon River, Heathcote River and the Avon/Heathcote Estuary. On Banks Peninsula, there are overflows at Lyttelton, Diamond Harbour, Governors Bay and Akaroa.

The previous consent focussed on reducing the frequency of overflows to waterways. However, there is only a limited link between the frequency of overflows and the effects on the waterways.

For this consent the Council plans to take more of an effects-based approach. We will focus on the values of the waterways, the effects of the overflows on those values, and therefore how we are best to reduce those effects.

The consent process will involve extensive consultation with key stakeholders, including the rūnanga and the wider community. Presentations to key stakeholders and the community have been given:

Current water quality

We all want to improve the quality of our waterways and we need to work out the best way to do that. It might be that we will get better outcomes by reducing contaminants in stormwater, rather than spending a lot of money reducing wastewater overflows. For example, to eliminate wastewater overflows altogether would require converting most of the city to a pressure sewer system, and would cost more than $3 billion to build. However, it would not necessarily result in an improvement in water quality.

The Council carries out extensive monitoring of the water quality in our waterways and in the past year has collected and analysed over 7,000 water quality samples.

The key contaminants were:

Sediment - the main contributor for poor water quality, which smothers habitat and food and can be contaminated. This comes from runoff from construction sites, unstabilised surfaces, vehicles and earthquakes.

Metals (zinc and copper) - toxic to fish and other creatures. These come mainly from brake pads, tyres and building products (roofs, spouting and downpipes).

Bacteria - create a public health risk. Bacteria mostly come from ducks and dogs, and occasionally from wastewater overflows.

Nutrients (nitrogen and phosphorus) - can be toxic (e.g. ammonia) and can encourage the growth of weeds and algae. Nutrients come from fertiliser, soils, and the faeces of livestock, dogs and ducks.

Most water quality monitoring sites show no change since 2007 and following the removal of large amounts of sediment, the waterways have been returned to prequake environments. The Council has prepared a water quality monitoring report for 2016 and previous years.

Improving waterways in Christchurch

The Council plans to spend more than $212 million over the next 10 years on projects to improve water quality:

Reducing wastewater overflows

The Council has already done a lot to reduce wastewater overflows:

Rubber flaps on constructed overflows stop river water getting into our wastewater pipes during floods

In flood prone areas, the vents on our manholes are being replaced with solid lids so stormwater ponding on the road does not get into wastewater pipes

In flood prone areas, plastic lids are being put on household gully traps, so that stormwater on private properties does not get into wastewater pipes

In Diamond Harbour and Lyttelton, a house to house survey has identified where property owners need to do repairs to stop stormwater getting into our wastewater system. Akaroa and Governors Bay will be targeted netxt.

The Council has completed the $150 million Major Sewer Upgrade project.

These measures, combined with low groundwater levels due to dry winters, mean that there has only been three wet weather overflow in the past two years in Christchurch city. This is already better than most cities in New Zealand and around the world. The Council maintains a list of recent wastewater overflows.

What you can do

Improving the quality of our waterways can’t be done by the Council alone – it needs to be done by the whole community. There are several things that you can do:

Avoid flushing wet wipes down the toilet. They are not flushable, no matter what they say on the packaging. Flushing wet wipes and other items causes blockages and overflows.

Put fat from cooking in the green organics bin rather than down the kitchen sink. Otherwise it congeals in the pipes and causes blockages and overflows.

Do not feed ducks. They are a major source of faecal contamination in waterways.

Pick up your dog's faeces and dispose of it in the red rubbish bin. This is a major source of faecal contamination in waterways.

Wash your paint brushes in the laundry tub so that the wash water does not go through stormwater drains into waterways.

Do not drop cigarette buts and other rubbish into drains and gutters.

Choose roofing materials that don’t contaminate our waterways – non-steel products or new condition powder coated steel are best. Unpainted galvanised roofs are the biggest source of zinc in our waterways. Make sure galvanised steel roofs are painted and the paint is in good condition.

Avoid copper spouting, downpipes and roofs. These are becoming a significant source of copper in waterways.

Next time your car needs new brakepads, ask for copper-free brakepads.

If you are building a new house, make sure that there are good erosion and sediment control measures in place to stop sediment washing off your property into waterways.